1. Field of the Invention
The present invention relates to image recording using exposure technology. More specifically, this invention relates to a focal position adjusting apparatus capable of appropriately forming an image focusing light beam at a predetermined position in multi-channel image exposure, and an exposure head and an image recording apparatus using the same.
2. Description of the Related Art
In various printers and copying machines, etc., an exposure apparatus is used, which performs scanning exposure on a photosensitive material, such as a silver salt photographic photosensitive material or an electro-photographic photosensitive material, using a recording light modulated in accordance with an image to be recorded.
At present, the dominating exposure apparatus is popular which performs, so-called, light beam scanning exposure. In such an exposure apparatus, a light beam modulated in accordance with the image to be recorded is deflected to a main scanning direction. The relative movement between the photosensitive material and the light beam is effected in a sub scanning direction being perpendicular to the main scanning direction, so that two-dimensional scanning exposure of the photosensitive material by the light beam is effected thereby recording the image.
Accompanying with improvement of recent technology in this field, it has become possible to rapidly record a high quality image by such light beam scanning exposure. However, image exposure by light beam scanning has limitation to increasing of image exposure speed and improvement in resolution. Particularly, in the case of forming a large image, which will find a large range of uses in the field of printing or the like, it is rather difficult to rapidly record an image of higher quality using image exposure by light beam scanning.
As a method of overcoming such a problem to make it possible to rapidly perform high quality image recording, a multi-channel image exposure technique is known, according to which exposure is simultaneously effected on a photosensitive material with a plurality of light beams, i.e., multi-beam modulated independently.
As schematically shown in FIG. 7, in such a multi-beam image exposure technique, an image is usually formed at a predetermined exposure position (recorded surface) X with all the light beams L (indicated by dashed lines) using a single image formation lens (image formation lens unit) 100.
Further, when a focal position adjusting function is introduced into the multi-beam exposure optical system, the image formation lens 100 is moved toward in the optical axis direction as indicated by the dotted lines in the drawing, so that the focal position of the light beams L is adjusted.
However, in this method, any difference in image forming position between the light beams (individual channels) cannot be corrected. A light beam occurs, which does not accurately form an image at the exposure position X, even if focal position adjustment is performed. Also even when the image formation lens 100 is inclined with respect to the optical axis due to assembly error, there is difference in focal position adjustment amount between the light beams, owing that a light beam occurs, which does not accurately form an image at the exposure position X.
Such difference in image forming condition between the light beams at the exposure position X will lead to a deterioration of image quality, such as image blurring.
In order to overcome the above problem of the above conventional art, it is an object of the present invention to provide a focal position adjusting apparatus which, in multi-beam exposure using a plurality of light beams, accurately performs focal position adjustment independently on each light beam (each channel), thereby making it possible to correct exposure using all the light beams. The present invention further has an object to provide a multi-channel exposure head utilizing this focal position adjusting apparatus, and an image recording apparatus utilizing such an exposure head.
According to a first aspect of this invention, a focal position adjusting apparatus is provided, comprising: a lens which converges electromagnetic wave to a focal position; first electrodes fixed to the lens; second electrodes being opposed which spacingly sandwiches each of the first electrodes, in an optical axis direction of the lens; and a biasing unit which biases the lens in a direction of an attractive force caused by static electricity between the first electrodes and the second electrodes caused by applying variable voltage to the first electrodes and the second electrodes.
Further it is preferable in the first aspect that the focal position adjusting apparatus, the lens being displaced using the force caused by the static electricity in the optical axis direction thereby adjusting the focal position on which the electromagnetic wave is converged.
Further it is preferable in the first aspect that the focal position adjusting apparatus according to claim 1, the biasing device being formed by a third electrode arranged on the opposite side of the second electrodes which are sandwiched by the first electrodes.
Further it is preferable in the first aspect that the focal position adjusting apparatus, the biasing device being formed by an elastic member and a power supply which applies voltage across the first electrodes and the second electrodes and a third electrode.
Further it is preferable in the first aspect that the focal position adjusting apparatus, the first and second electrodes and the opposed electrodes being ring-shaped.
Further it is preferable in the first aspect that the focal position adjusting apparatus is plurally arranged.
According to a second aspect of this invention, an exposure head is provided, comprising a focal position adjusting apparatus being plurally arranged, including: a lens which converges electromagnetic wave to a focal position; first electrodes fixed to the lens; second electrodes being opposed which spacingly sandwiches the first electrodes in an optical axis direction of the lens; and a biasing unit which biases the lens in a direction of an attractive force caused by static electricity between the first electrodes and the second electrodes caused by applying variable voltage to the first electrodes and the second electrodes, and a light source section which makes light beams incident on one lens or more of the focal position adjusting apparatus and which can modulate each of light beams independently.
According to a second aspect of this invention, an exposure head is provided comprising: an exposure head; and a scanning unit; the exposure head having a focal position adjusting apparatus being plurally arranged including, a lens which converges electromagnetic wave to a focal position; first electrodes fixed to the lens; second electrodes being opposed which spacingly sandwiches the first electrodes, in an optical axis direction of the lens; and a biasing unit which biases the lens in a direction of an attractive force caused by static electricity by applying variable voltage to the first electrodes and the second electrodes, and a light source section which making light beams incident on one lens or more of the focal position adjusting apparatus and which can modulate each of light beams independently, and the scanning unit displacing a photosensitive material with relative to the exposure head.